1. Field of the Invention
The present invention relates to optical disk apparatuses, methods of controlling the apparatuses, and programs. More particularly, the present invention relates to an optical disk apparatus, a method of controlling the optical disk apparatus, and a program capable of rapidly adjusting a tile angle indicating a tilt of the optical axis of a pickup irradiating an optical disk with laser light. The optical disk has multiple, for example, two recording layers on one side.
2. Description of the Related Art
Optical disks that are irradiated with laser light to record and play back data include compact discs (CDs), digital versatile disks (DVDs), and magneto-optical (MO) disks.
High-capacity and high-density optical disks called Blu-ray (Registered trademark) discs (hereinafter also referred to as BDs) have been put to practical use in recent years.
The BDs include Blu-ray discs-Read Only Memory (BD-ROMs) used only for playback, Blu-ray discs-Recordable (BD-Rs) on which data can be recorded only once, and Blu-ray discs-Rewritable (BD-RWs) on which data can be recorded multiple times.
Optical disks having multiple, for example, two recording layers are made practical in order to further increase the recording capacities of the optical disks. Of the two recording layers, a recording layer near the cover layer is called an “L1” layer and a recording layer far from the cover layer is called an “L0” layer.
In such an optical disk apparatus that records data on an optical disk and plays back data on the optical disk, if the optical axis of the (optical) pickup (the optical axis of laser light), which irradiates the optical disk with the laser light and receives reflected light of the laser light to output a radio-frequency (RF) signal etc., does not form an appropriate angle (for example, an angle of 90°) with the recording layer of the optical disk, the spot of the laser light on the recording layer of the optical disk can be distorted to prevent normal playback or recording.
In order to resolve such a problem, the optical disk apparatus performs a startup process to, for example, adjust the tilt angle indicating the tilt of the optical axis of the laser light emitted from the pickup to an optimal tilt angle when, for example, the optical disk is loaded in the optical disk apparatus.
Specifically, in the startup process, the optical disk apparatus adjusts the tilt angle at a position toward the inner circumference of the optical disk to detect an optimal tilt angle toward the inner circumference (an inner-circumference-side optimal tilt angle) and adjusts the tilt angle at a position toward the outer circumference of the optical disk to detect an optimal tilt angle toward the outer circumference (an outer-circumference-side optimal tilt angle).
In recording or playback, the optical disk apparatus calculates the optimal tilt angle at each position in the radial direction of the optical disk by interpolation using the inner-circumference-side optimal tilt angle and the outer-circumference-side optimal tilt angle to control the tilt angle so as to be equal to the optimal tilt angle at the position where the recording or playback is performed on the optical disk.
In other words, the (radial) tilt angle of the objective lens (the tilt of the optical axis of the objective lens) of the pickup is controlled in the optical disk apparatus.
The control described above allows the optical disk apparatus to perform the normal playback or recording even if optical disks that are used are individually varied or the curvature of the optical disks are varied across the ages.
In a typical DVD having the two layers: the “L0” layer and the “L1” layer on one side, the distance from (the surface opposing the pickup of) the cover layer to the “L0” layer is around 0.6 mm and the distance from the cover layer to the “L1” layer is around 90% of the distance from the cover layer to the “L0” layer. Accordingly, the ratio between the distance from the cover layer to the “L0” layer and the distance from the cover layer to the “L1” layer is about 10:9, which is close to 1:1. In other words, the distance to the “L0” layer with respect to the pickup is approximately the same as that to the “L1” layer with respect to the pickup.
In addition, as for the DVD, the numerical aperture (NA) of the objective lens of the pickup is not so high (around 0.6).
For the above reasons, when the pickup forms a certain angle with the DVD (when the optical axis of the pickup forms a certain angle with the recording layer of the optical disk), the spot of the laser light formed on one of the “L0” layer and the “L1” layer has the same shape as the spot of the laser light formed on the other layer.
Consequently, in the DVD having the two layers: the “L0” layer and the “L1” layer on one side, the optimal tilt angle detected by adjusting the tilt angle with respect to only one of the “L0” layer and the “L1” layer can be used for the other layer. Accordingly, it is sufficient to detect the optimal tilt angle with respect to only one of the “L0” layer and the “L1” layer and it is not necessary to detect the optimal tilt angle with respect to the other layer.
However, technologies for adjusting the tilt angle with respect to each of multiple recording layers on a DVD to detect an optimal tilt angle at which an RF signal output from the pickup has the largest amplitude are proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2007-095151).
The degree of a variation in amplitude of an RF signal with respect to a variation in tilt (in the radial direction) of a typical DVD (hereinafter referred to as a disk tilt sensitivity) coincides with the degree of a variation in amplitude of the RF signal with respect to a variation in tilt (in the radial direction of the optical axis) of the pickup (hereinafter referred to as a lens tilt sensitivity) whereas the disk tilt sensitivity does not coincide with the lens tilt sensitivity in a typical BD.